This invention generally relates to mechanisms for steering boats and other watercraft. In particular, the invention relates to mechanisms for steering jet-powered watercraft.
It is known to propel a boat or other watercraft using a water jet apparatus, with the powerhead placed inside (inboard) or outside (outboard) the hull and an axial-flow water jet apparatus mounted outside the hull below the waterline. The drive shaft of the water jet apparatus is coupled to the crankshaft of the motor. The water jet apparatus comprises an impeller mounted on the drive shaft and a housing surrounding the impeller. The interior surface of the housing defines a water tunnel. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the water tunnel and out an exit nozzle. The reaction force of the rearward water flow exiting the jet propulsion device propels the watercraft forward.
To facilitate use of jet-propelled boats in shallow water, it is known to mount the water jet propulsion unit at an elevation such that the propulsion unit does not project below the bottom of the boat hull. This can be accomplished, for example, by installing a duct in the stern of the boat, the duct being arranged to connect one or more inlet holes formed in the bottom of the hull with an outlet hole formed in the transom. The water jet propulsion unit is then installed outside the hull in a position such that the inlet of the water jet propulsion unit is in flow communication with the duct outlet at the transom.
Typically, a jet-propelled watercraft generates forward thrust by impelling water rearward out a discharge end of a water jet propulsion unit. Directional control is provided by turning a steering nozzle pivotably mounted at the discharge end of the water jet propulsion unit. The steering position of the steering nozzle is controlled by the operator by manipulation of a steering wheel (in the case of a boat) or handlebars (in the case of a personal watercraft). The turned steering nozzle deflects discharging water flow to one side, generating a lateral thrust which pushes the stern of the boat or watercraft in the opposite direction. This in turn causes the bow of the boat or watercraft to turn toward the side to which the steering nozzle is aimed.
This type of steering arrangement is effective only when the thrust produced by the water jet propulsion unit is greater than a minimum controllable steering thrust. Releasing the throttle causes the vessel to go straight, even if the steering wheel or handlebars are turned, because little or no water discharged rearward results in little or no steering thrust when that discharged water is diverted by the steering nozzle. Turns cannot be made without applying throttle (i.e., thrust).
Some water jet propulsion applications have added a rudder to the steering nozzle to overcome the foregoing problem. However, at any level other than low thrust, a rudder is not required for steering and is a disadvantage in at least two respects. First, a steering rudder must be submerged in the body of water in which the watercraft is operating in order to effect steering. When the steering rudder is submerged, it can be subject to damage. The increased draft of the submerged rudder limits shallow water operation. Second, the steering rudder also increases drag during high-speed operation. This lowers the top speed of the watercraft.
There is a need for a steering arrangement which would overcome the foregoing disadvantages while still allowing low-thrust (i.e., idle, neutral and reverse) steering control.
The present invention is directed to a jet-powered watercraft in which the water jet propulsion unit has a retractable rudder mounted on the steering nozzle. The steering nozzle is pivotably mounted to the housing of the water jet propulsion unit, with a generally vertical pivot axis. The rudder is pivotable relative to the steering nozzle about a generally horizontal axis, between a retracted position, where the rudder extends out of the water, and a down position, where the rudder is submerged in the water. Preferably the rudder does not pivot relative to the steering nozzle about a generally vertical axis, but rather is turned in unison with the steering nozzle as the latter is pivoted about the generally vertical pivot axis.
In accordance with the preferred embodiments of the invention, the rudder position is controlled as a function of the power being output by the engine. In particular, means are provided for changing the angular position of the rudder when the revolutions per unit time of the powerhead reach a predetermined threshold, e.g., pivoting the rudder from the down position to the retracted position when the powerhead rpm level exceeds the predetermined threshold. In one embodiment, the revolutions per unit time of the drive shaft are detected. In another embodiment, the control position (which may be arrived at via either translation or rotation) of the operator throttle control device is detected. Pivoting of the rudder may be actuated by a solenoid, a hydraulic cylinder or any other functionally equivalent electrical, mechanical or electromechanical device. Alternatively, the rudder can be coupled to the operator""s throttle by means of a mechanical linkage or cable.
When the water jet propulsion unit is operated with less than a minimum controllable steering thrust, the rudder is submerged in the water and the watercraft can be steered using the rudder to generate a steering force when the steering nozzle is turned. When the rudder is down, the operator can control the direction of the watercraft by turning the steering wheel or handlebars even at low or no thrust. When the thrust produced by the water jet propulsion unit is greater than the minimum controllable steering thrust, the rudder is retracted, i.e., pivoted to the up position. In the latter case, the operator still controls the watercraft""s direction by turning the steering wheel or handlebars, but the steering force is provided by the water flow discharged from the steering nozzle rather than the rudder.
The present invention has utility in any water jet propulsion unit in which steering thrust is effected by redirecting discharge water flow. The powerhead which drives the water jet propulsion unit can be mounted either inboard or outboard of the boat hull.